You might need to end up replacing the other RAM chips.
Also, if its timed to HD activity, that would strongly suggest analog board instability. If it isn't recapped, it should be. Without the video issue, the analog board instability would most likely show up as a screen "wobble" when the HD is active.
Also, if its timed to HD activity, that would strongly suggest analog board instability. If it isn't recapped, it should be. Without the video issue, the analog board instability would most likely show up as a screen "wobble" when the HD is active.